Several standard protocols for wireless local area networks, commonly referred to as WLANs, are becoming popular. These include protocols such as 802.11 (as set forth in the 802.11 wireless standards), Wi-MAX, and Bluetooth. The standard wireless protocol with the most commercial success to date is the 802.11g protocol.
While the specifications of products utilizing the above standard wireless protocols commonly indicate data rates on the order of, for example, 54 MBPS and ranges on the order of, for example, 100 meters, these performance levels are rarely, if ever, realized. This lack of performance is due to attenuation of the radiation paths of RF signals, which are typically in the range of 2.4 GHz, in an indoor environment. Base to receiver ranges are generally less than the coverage range required in a typical home, and may be as little as 10 to 15 meters. Further, in structures that have split floor plans, such as ranch style or two story homes, or that are constructed of materials that attenuate RF signals, areas in which wireless coverage is needed may be physically separated by distances outside of the range of, for example, an 802.11 protocol based system. Finally, the data rates of the above standard wireless protocols are dependent on the signal strength. As distances in the area of coverage increase, wireless system performance typically decreases.
One way to increase the range of wireless systems is by the use of repeaters. This is a common practice in the mobile wireless industry. One significant complication is that the system receivers and transmitters operate at the same frequency for a WLAN utilizing an 802.11 or an 802.16 WMAN wireless protocol. Such operation is commonly referred to as time division duplexing (TDD). This operation is significantly different than the operation of many cellular repeater systems, such as those systems based on IS-136, IS-95 or IS-2000 standards, where the receive and transmit bands are separated by a duplexing frequency offset. Frequency division duplexing makes the repeater operation easier than in the case where the receiver and transmitter channels are on the same frequency.
There are, however, cellular mobile systems that separate the receive and transmit channels by time rather than by frequency. These systems utilize scheduled times for specific uplink/downlink transmissions. Repeaters for these systems are more easily built, as the transmission and reception times are well known and are broadcast by a base station. Receivers and transmitters for these systems may be isolated by any number of means including physical separation, antenna patterns, or polarization isolation.
The random packet nature of the WLAN protocols provides no defined receive and transmit periods. The packets from each wireless network node are spontaneously generated and transmitted and are not temporally predictable. A protocol referred to as a collision avoidance and random back-off protocol is used to avoid two units transmitting their packets at the same time. For an 802.11 standard protocol, this is referred to as the distributed coordination function (DCF). In the case where the receive and transmit times are known, synchronization of the timing can be problematic and can drive up the expense of the product.
WLAN repeaters have unique constraints due to the above spontaneous transmission capabilities and therefore require a unique solution. Another unique requirement is that, since these repeaters use the same frequency for receive and transmit, some form of isolation must exist between the receiver and transmitter of each repeater. While existing CDMA systems employ directional antennas and physical separation of the receive and transmit antennas to achieve this isolation, such techniques are not practical for WLAN repeaters in many operating environments such as in the home where lengthy cabling is not desirable or may be too costly.
Further, in a WLAN environment utilizing the proposed IEEE 802.11n standard protocol, wireless devices rely on multi-path transmissions to increase data rates and range. However, in a typical home WLAN environment, multi-path transmission capability and spatial diversity are limited for many of the same reasons discussed above in connection with lack of performance of wireless products in a home or indoor environment.